Cancer immunotherapy provides a promising outlook for the treatment of many cancers. However, tumors have developed strategies to suppress immunity through the formation of immunosuppressive cells, such as regulatory T cells and MDSCs, which can in turn suppress immune effector cells and secrete more immunosuppressive cytokines into the tumor microenvironment. Therefore, the need for a strong therapy to elicit an anti-tumor immune response to overcome any immunosuppressive factors is evident. The particulate natured virus-like particles (VLPs) have been shown to induce a strong immune response, and thus present as a promising tool to overcome immunosuppression by tumors. This proposal studies the incorporation of glycosyl-phosphatidylinositol (GPI)-anchored tumor associated antigens (GPI-TAAs) along with GPI-anchored immunostimulatory molecules (GPI-ISMs), such as cytokines, costimulatory molecules, and adhesion molecules, onto the surface of lipid enveloped VLPs, such as influenza VLPs, by a novel protein transfer approach. The association of TAAs on the surface of VLPs will allow the immune response to be directed against these TAAs that are also associated on tumor cells, whereas the addition of ISMs on the VLP surface along with the TAAs will allow for increased uptake and presentation of the VLPs as well as enhanced activation of antigen presenting cells. Furthermore, inclusion of GPI-cytokines on the surface of VLPs allows for a slow release depot at the immunization site, thus increasing the efficacy of the vaccine. This protein transfer approach requires the use of GPI-anchored proteins to be incubated with enveloped VLPs at 37oC for a short incubation time. Upon incubation, spontaneous incorporation of the GPI-proteins onto the lipid bilayer of the VLPs occurs. This protein transfer method allows us to overcome any cytopathological effects induced when genetically modifying VLPs to express proteins. Thus, this approach also allows for the incorporation of many GPI-proteins onto the same VLP simultaneously and the expression levels of the GPI-proteins can be easily controlled. After production of the resulting chimeric VLPs, we intend to study the efficacy of these protein transferred-VLPs in eliciting tumor regression in mice with established tumors and study the immune correlates that lead to regression by analyzing cellular and humoral immune responses. We will be using a 4T07 murine breast cancer model transfected to express the TAA, HER-2, for these studies. Therefore, we propose to incorporate GPI-HER-2 and GPI-ISMs onto the surface of enveloped VLPs by protein transfer to enhance antitumor immune responses and tumor regression in mice with established tumors. The knowledge obtained from these studies will form a foundation to develop VLP-based efficacious therapeutic cancer vaccines to treat existing tumors or lead to the prevention of metastatic growth in humans.